Switching system linked to radio base station

ABSTRACT

A switching system includes N handover runks respectively having M terminals to be independently coupled to radio transmission lines reaching M radio base stations which respectively form radio zones which become mutually adjacent zones or peripheral zones, and coupled to remote transmission lines reaching mobile stations of other parties located in the radio zones, where M and N are integers greater than one, out of the radio transmission lines, the N handover trunks selecting each transmission line with a best transmission quality and coupling the selected radio transmission lines to the remote transmission lines; a plurality of radio interfaces distributing lines independently formed between the switching system and the M radio base stations, with respect to different N paths; a radio transmission line forming unit forming radio transmission lines in advance with respect to all combinations of each of the paths subject to the distribution by the radio interfaces and each of the terminals other than the terminals to be independently coupled to the remote transmission lines out of the terminals of the handover trunks; a call processing unit carrying out a call processing with respect to calls generated by the mobile stations located in the radio zones by cooperating with a radio channel setting control that is carried out by the radio base stations via the radio interfaces; and a remote transmission line forming unit forming the remote transmission lines by the call processing carried out by the call processing unit.

BACKGROUND OF THE INVENTION

The present invention generally relates to switching systems, and moreparticularly to a switching system which is connected via a link to aradio base station of a mobile communication system that carries outswitching of channels in service, and processes calls generated in themobile communication system.

The Code Division Multiple Access (CDMA) was frequently used incommunication for military purposes because the CDMA has a superiorsecrecy and is strong against interference. However, by positivelyutilizing the strong anti-interference characteristic of the CDMA, it ispossible in general to improve the utilization efficiency of radiofrequencies. In addition, since techniques for realizing a transmissionpower control with a high accuracy and an improved response have beenestablished recently, the CDMA is now being applied to mobilecommunication systems in which mobile stations scattered in radio zonesmove while maintaining a service state and the switching of the channelsin service, that is, handover of the channels, is carried out.

In the mobile communication system applied with the CDMA, the levels ofthe received waves reaching the base stations of the adjacent radiozones from the mobile station which is the subject of the handover areappropriately varied under the transmission power control describedabove. For this reason, unlike the mobile communication systems appliedwith the Time Division Multiple Access (TDMA) or the Frequency DivisionMultiple Access (FDMA), the radio zone to which the handover is to bemade cannot be determined to a single radio zone depending on the levelsof the received waves.

Accordingly, in the mobile communication system applied with the CDMAuses an Asynchronous Transfer Mode (ATM) switching system which cansmoothly and dynamically switch the radio zone to the radio zone handedover with the call. The ATM switching system and each radio base stationare connected via a link adapted to the ATM.

However, in the mobile communication system applied with the CDMA, itwas difficult to use a conventional ATM switching system without greatlymodifying the construction of the conventional ATM switching system.

In addition, a delay in updating identification information related tothe handover causes considerable deterioration of the speech quality,and it was particularly difficult to apply the conventional ATMswitching system to a call of a telephone system in the mobilecommunication system.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful switching system in which the problems describedabove are eliminated.

Another and more specific object of the present invention is to providea switching system which can flexibly cope with frequent generation ofhandovers, without requiring a considerable modification of hardware.

Still another object of the present invention is to provide a switchingsystem comprising N handover trunks respectively having M terminals tobe independently coupled to radio transmission lines reaching M radiobase stations which respectively form radio zones which become mutuallyadjacent zones or peripheral zones, and coupled to remote transmissionlines reaching mobile stations of other parties located in the radiozones, where M and N are integers greater than one, out of the radiotransmission lines, the N handover trunks selecting each transmissionline with a best transmission quality and coupling the selected radiotransmission lines to the remote transmission lines; a plurality ofradio interfaces distributing lines independently formed between theswitching system and the M radio base stations, with respect todifferent N paths; a radio transmission line forming unit forming radiotransmission lines in advance with respect to all combinations of eachof the paths subject to the distribution by the radio interfaces andeach of the terminals other than the terminals to be independentlycoupled to the remote transmission lines out of the terminals of thehandover trunks; a call processing unit carrying out a call processingwith respect to calls generated by the mobile stations located in theradio zones by cooperating with a radio channel setting control that iscarried out by the radio base stations via the radio interfaces; and aremote transmission line forming unit forming the remote transmissionlines by the call processing carried out by the call processing unit.According to the switching system of the present invention, theselection of the radio transmission line having the best transmissionquality is automatically selected by the handover trunks from the radiotransmission lines which are formed in advance by the radio transmissionline forming unit. For this reason, compared to a case where the radiotransmission line is dynamically set by the call processing, the load ofthe process of switching the transmission lines when making the handoveris positively distributed among the handover trunks.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system block diagram showing the construction of aconceivable ATM switching system applied to a mobile communicationsystem;

FIG. 2A is a diagram showing the format of a standard cell;

FIG. 2B is a diagram showing the format of a partial filling cell;

FIG. 3 is a system block diagram for explaining the operating principleof the present invention;

FIG. 4 is a system block diagram showing an embodiment of a switchingsystem according to the present invention;

FIG. 5 is a system block diagram showing an embodiment of a handovertrunk;

FIG. 6 is a time chart for explaining the operation of the embodiment ofthe switching system;

FIG. 7 is a time chart for explaining the operation of the embodiment ofthe switching system;

FIG. 8 is a diagram showing the construction of a radio PVC table;

FIG. 9 is a diagram showing the construction of a radio line table:

FIG. 10 is a diagram showing the construction of a fixed line table;

FIG. 11 is a diagram for explaining an embodiment of a PVC formed in theembodiment of the switching system; and

FIG. 12 is a system block diagram showing a communication system appliedwith the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a description will be given of a conceivable ATM switching systemin order to facilitate the understanding of the present invention. FIG.1 is a system block diagram showing the construction of a conceivableATM switching system applied to a mobile communication system.

In FIG. 1, a radio base station (not shown) is connected to amultiplexing/demultiplexing unit 71 via a full-duplex line.Demultiplexed outputs of the multiplexing/demultiplexing unit 71 arerespectively connected to up-terminals of corresponding ports of an ATMswitch 73 via header converters (HCV) 72_(u1) through 72_(um), anddown-terminals of these ports of the ATM switch 73 are connected tocorresponding multiplexing inputs of the multiplexing/demultiplexingunit 71. Down-terminals of other m ports (hereinafter referred to ashandoff ports,) of the ATM switch 73 are connected to correspondinginputs of handover trunks 74₁ through 74_(m). Outputs of the handovertrunks 74₁ through 74_(m) forming pairs with the inputs of the handovertrunks 74₁ through 74_(m) are connected to up-terminals of the handoffports of the ATM switch 73 via header converters (HCV) 72_(d1) through72_(dm). Control terminals of the header converters 72_(ul) through72_(um), the header converters 72_(d1) through 72_(dm), the ATM switch73, and the handover trunks 74₁ through 74_(m) are connected tocorresponding output (communication) ports of a processor 76.

In the mobile communication system applied with the ATM switching systemhaving the construction shown in FIG. 1, the radio base stationgenerates a standard cell shown in FIG. 2A with respect to each radiochannel which is allocated by the radio base station based on apredetermined radio channel setting control procedure, and transmits thestandard cell to a logical channel. As shown in FIG. 2A, the standardcell includes a header, and one or a plurality of short cells. The shortcell includes a short cell header and a payload. In the short cell, theshort cell header indicates a base station identification informationLLN, and reliability information which indidates a transmission qualityof the radio transmission line evaluated by the radio base station. Aword indicating a received call signal is arranged in the payload. Theheader of the standard cell indicates identification information of thelogical channel that is formed in advance as a transmission line for theshort cell, in an up-link of the full-duplex line described above. Thisidentification information of the logical channel includes a VirtualPath Identifier (VPI) and a Virtual Channel Identifier (VCI).

The multiplexing/demultiplexing unit 71 forms in advance physicalchannels corresponding to each of the base station identificationinformation LLN₁ through LLN_(m) which may be transmitted from the radiobase station, between the multiplexing/-demultiplexing unit 71 and theheader converters 72_(u1) through 72_(um).

In addition, when the standard cell described above is received from theradio base station, the multiplexing/demultiplexing unit 71 divides thestandard cell into units of short cells based on the format shown inFIG. 2A, and adds pseudo bits of a predetermined length to the shortcell so as to generate a sequence of partial filling cells each havingthe same word length as the word length of the standard cell as shown inFIG. 2B. The multiplexing/demultiplexing unit 71 also transmits thepartial filling cells to the physical channels described above.

The header converters 72_(u1) through 72_(um) read the partial fillingcells which are obtained via the physical channels, and with respect tothe partial filling cells, carries out a process of converting theheader to the identification information of the logical channels givenby the processor 76 according to the call processing procedure beforetransmitting the partial filling cells to the corresponding ports of theATM switch 73. In this case, the identification information is(VPI_(p1), VCI_(p1)) through (VPI_(pm), VCI_(pm)) and indicates theports of the ATM switch 73 to which the header converters 72_(u1)through 72_(um) are connected.

The above described ports of the ATM switch 73 are connected to theinputs of the handover trunks 74₁ through 74_(m) via paths which areformed in the ATM switch 73 based on a line switching system.Furthermore, the inputs of the handover trunks 74₁ through 74_(m) areconnected via other paths which are similarly formed in the ATM switch73 by the call processing to an adjacent radio base station other thanthe radio base station described above, more particularly, to a trunk(not shown) which forms an interface adapted to a terminal of the otherparty or adapted to a transmission line between the stations.

A description related to communication channels formed in up-sectionfrom the above trunk to the handover trunks 74₁ through 74_(m), and indown-sections from the handover trunks 74₁ through 74_(m) to the radiobase station described above via the header converters 72_(d1) through72_(dm), the ATM switch 73 and the multiplexing/-demultiplexing unit 71,will be omitted due to the reversibility of the full-duplex line.

The header converters 72_(u1) through 72_(um) cooperate with the radiochannel setting control that is carried out by the radio base stationdescribed above to realize the handover and the call processingdescribed above, and successively adapt to an updated result when theidentification information of the logical channel given in advance bythe processor 76 is updated. Accordingly, the handover trunks 74₁through 74_(m) form the parallel transmission lines for the call signalsbetween the handover trunks 74₁ through 74_(m) and a plurality of radiobase stations which can constantly secure a predetermined speech qualitydepending on the handover, via the header converters 72_(u1) through72_(um), the header converters 72_(d1) through 72_(dm), the ATM switch73 and the multiplexing/demultiplexing unit 71.

In addition, out of the partial filling cells obtained via the pluralityof transmission lines, the handover trunks 74₁ through 74_(m) comparereliability information included in the short cell headers andconstantly select the path corresponding to the radio transmission line(radio base station) having the best transmission quality.

Accordingly, the speech quality of the channels formed via the handovertrunks 74₁ through 74_(m) is maintained to a satisfactory quality whileadapting to the change in the transmission characteristic of the radiotransmission line and the movement of the mobile station, even when thetransmission power of the mobile station changes under the transmissionpower control.

Illustration and description related to a trunk which is used for theconnection to a public network are omitted in the above describedconceivable system, because such a trunk is not directly related to thesubject matter of the present invention which will be described later.

In the above described conceivable system, however, the processor 76which gives the identification information of the logical channels tothe header converters 72_(u1) through 72_(um) and the header converters72_(d1) through 72_(dm) must update the identification information everytime the handover is made, with respect to all of the completed calls.The number of times the identification information is updated isconsiderably large compared to that for a case where all of the mobilestations do not move. In the ATM transmission line having thetransmission rate of 150 Mbps, if the average holding time is threeminutes, 20 to 30 times per second is the upper limit of the number oftimes the identification information can be updated according to theexisting technique.

Therefore, in the mobile communication system applied with the CDMA, itis difficult to realize the conceivable ATM switching system withoutgreatly modifying the construction of a conventional ATM switchingsystem.

In addition, a delay in updating the identification information relatedto the handover causes considerable deterioration of the speech quality,and it is particularly difficult to apply the conceivable ATM switchingsystem to the call of the telephone system in the mobile communicationsystem.

Next, a description will be given of the operating principle of thepresent invention, by referring to FIG. 3.

In a switching system according to the present invention shown in FIG.3, N handover trunks 11₁ through 11_(N) respectively have M terminals tobe independently connected to radio transmission lines reaching M radiobase stations which respectively form radio zones which become mutuallyadjacent zones or peripheral zones, and to remote transmission linesreaching mobile stations of other parties located in the radio zones,where M and N are integers greater than one. Out of these radiotransmission lines, the N handover trunks 11₁ through 11_(N) select eachtransmission line with the best transmission quality and connect theselected radio transmission lines to the remote transmission lines. Mradio interfaces 12₁ through 12_(M) distribute the lines independentlyformed between the switching system and the M radio base stations, withrespect to different N paths. A radio transmission line forming unit 13forms radio transmission lines in advance with respect to allcombinations of each of the paths subject to the distribution by theradio interfaces 12₁ through 12_(M) and each of the terminals other thanthe terminals to be independently connected to the remote transmissionlines out of the terminals of the handover trunks 111 through 11_(N). Acall processing unit 14 carries out a call processing with respect tocalls generated by the mobile stations located in the radio zones bycooperating with a radio channel setting control that is carried out bythe radio base stations via the radio interfaces 12₁ through 12_(M). Aremote transmission line forming unit 15 forms the remote transmissionlines by the call processing carried out by the call processing unit 14.

According to this switching system, the selection of the radiotransmission line having the best transmission quality is automaticallyselected by the handover trunks 11₁ through 11_(N) from the radiotransmission lines which are formed in advance by the radio transmissionline forming unit 13. For this reason, compared to a case where theradio transmission line is dynamically set by the call processing, theload of the process of switching the transmission lines when making thehandover is positively distributed among the handover trunks 11₁ through11_(N).

The switching system described above may be provided with a storage unit21 which is registered in advance with a set of radio zonescorresponding to the adjacent zones or the peripheral zones, withrespect to each of the radio zones formed by the radio base stations. Inthis case, the call processing unit 14 obtains the radio zone where themobile station which generated the call is located or is predicted to belocated, with respect to each of the calls subject to the callprocessing. In addition, the call processing unit 14 notifies the radiozones registered in the storage unit 21 with respect to the obtainedradio zone to at least one of the handover trunks 11₁ through 11_(N)connected to the radio transmission line. The handover trunks 11₁through 11_(N) selects the radio transmission line having the besttransmission quality by limiting candidates to the radio transmissionlines corresponding to the radio zones notified by the call processingunit 14.

In this case, with respect to each of the calls allocated thereto, thehandover trunks 11₁ through 11_(N) compare the transmission qualities ofonly the transmission lines formed via the radio transmission lineforming unit 13 between the switching system and the radio zones wherethe mobile station which generated the call may be located. As a result,the load on the handover trunks 11₁ through 11_(N) is considerablyreduced, and it is possible to maintain a high transmission qualitywhile positively adapting to the handover that is frequently madedepending on the movements of the mobile stations.

In addition, in the switching system described above, the radiotransmission line forming unit 13 and the remote transmission lineforming unit 15 may be integrally formed as a single unit, so as to formthe radio transmission lines by the call processing carried out by thecall processing unit 14.

In this case, the radio transmission lines are formed by sharing theremote transmission line forming unit 15 which forms the remotetransmission lines. As a result, it is possible to flexibly adapt to thehandover that is frequency carried out, without modifying the hardwarestructure.

Moreover, in the switching system described above, the radiotransmission line forming unit 13 and the remote transmission lineforming unit 15 are formed independently as separate units, so as toautomatically form all of the radio transmission lines.

The remote transmission line forming unit 15 may not be able to form allof the radio transmission lines in advance within the range of thenumber of ports peculiar to the remote transmission line forming unit15. But even in such a case, the load of the remote transmission lineforming unit 15 and the call processing unit 14 can be positivelydistributed with respect to the handover trunks 11₁ through 11_(N) usingthe construction having radio transmission line forming unit 13 providedindependently of the remote transmission line forming unit 15. Inaddition, a high transmission quality can be maintained by adapting tothe handover that is frequently carried out.

Furthermore, in the switching system described above, an asynchronoustransfer mode may be applied to the plurality of lines formed betweenthe radio interfaces 12₁ through 12_(M) and the plurality of radio basestations, so that the radio transmission line forming unit 13 forms theradio transmission lines conforming to the asynchronous transfer mode.

In this case, uniform communication channels can be secured not only forthe calls in the telephone system but also the calls in the data system.In addition, the handover trunks 11₁ through 11_(N) can efficientlyselect the transmission lines by referring to headers of the cells intowhich the transmission information is divided.

Next, a description will be given of an embodiment of the switchingsystem according to the present invention.

FIG. 4 is a system block diagram showing this embodiment of theswitching system. In FIG. 4, those parts which are essentially the sameas those corresponding parts in FIG. 1 are designated by the samereference numerals, and a description thereof will be omitted. In FIG.4, a radio line control station 31 and a radio base station 32 areconnected to an ATM switching system 30 via communication links.

In the following description, it will be assumed for the sake ofconvenience that one radio line control station 31 and one radio basestation 32 are provided, so as to simplify the description.

The ATM switching system 30 shown in FIG. 4 differs from the switchingsystem shown in FIG. 1 in that a multiplexing/demultiplexing unit 71a isprovided in place of the multiplexing/demultiplexing unit 71, and theradio line control stations 31 (only one shown in FIG. 4) are connectedto the multiplexing/demultiplexing unit 71a via independent lines. Inaddition, header converters 72_(l1) through 72_(lN), . . . , 72_(M1)through 72_(MN) and header converters 79_(l1) through 79_(lM), . . . ,79_(M1) through 79_(MM) are provided in place of the header converters72_(u1) through 72_(um), . . . , 72_(d1) through 72_(dm). Handovertrunks 74a₁ through 74a_(N) are provided in place of the handover trunks74₁ through 74_(m), and a processor 76a is provided in place of theprocessor 76.

The header converters 72_(l1) through 72_(lN), . . . , 72_(M1) through72_(MN) respectively are integrally formed by a combination of headerconverters corresponding to the up-link and the down-link, such as thecombination of the header converters 72_(u1) and 72_(d1) in the case ofthe switching system shown in FIG. 1, for example, and the headerconverters 79_(l1) through 79_(lM), . . . , 79_(M1) through 79_(MM)respectively are integrally formed by a similar combination.

The radio line control station 31 includes an external interface (EIF)33 connected to the lines described above, a transmission line interface(HIF) 34 connected to a digital link which is formed between the radioline control station 31 and the radio base station 32, a switch part(SW) 35 interposed between the transmission line interface 34 and theexternal interface 33, and a radio controller (RCNT) 36 which isconnected to control terminals of the external interface 33, thetransmission line interface 34 and the switch part 35.

The radio base station 32 includes a transmission line interface (HIF)37 connected to the digital link which is formed between the radio linecontrol station 31 and the radio base station 32, a baseband signalprocessor (BB) 39, a radio unit (TRX) 40 and a transmission/receptionamplifier (AMP) 41 which are connected in series between thetransmission line interface 37 and a power supply end of an antenna 38,and a controller (BCNT) 42 connected to control terminals of thetransmission line interface 37, the baseband signal processor 39, theradio unit 40 and the transmission/reception amplifier 41.

FIG. 5 is a system block diagram showing an embodiment of the handovertrunk 74a₁. As shown in FIG. 5, the handover trunk 74a₁ includes a lineinterface (INRF) 51d, a line interface (INFS) 51u, a cell extractionunit (DROP) 52, a cell buffer (BUFF) 53, a cell converter (INS) 54, aquality information comparator (QCMP) 55, a write controller (WC) 56, acell information manager (IMNG) 57, a read controller (RC) 58, a buffermanager (BMNG) 59, an address converter (ADCV) 60, a header converter(HCV) 61, a cell identifier (CHCV) 62, and a controller 63.

The line interface 51d is connected to up-lines and down-lines formed bycorresponding ports of the ATM switch 73a. The cell extraction unit 52,the cell buffer 53 and the cell converter 53 are connected in seriesbetween the line interfaces 51d and 51u. The quality informationcomparator 55 is connected to a quality information output terminal ofthe cell extraction unit 52 and a quality information input terminal ofthe cell buffer 53. The write controller 57, the cell informationmanager 57 and the read controller 58 are connected in series between acontrol output of the cell extraction unit 52 and a control input of thecell converter 54. The buffer manager 59 is connected to controlterminals of the write controller 56 and the read controller 58. Theaddress converter 60 is connected to an output terminal of the buffermanager 59 and between address output terminals of the write controller56 and the read controller 58 and two address inputs of the cell buffer53. The header converter 61 is arranged between the address outputterminal of the read controller 58 and a header input terminal of thecell converter 54. The cell identifier 62 is arranged between an addressoutput of the cell extraction unit 52 and address inputs of the writecontroller 56 and the read controller 58. The controller 63 is connectedto the processor 76a via a communication link and generally controlseach of the parts 51d through 62 forming the handover trunk 74a₁.

In this embodiment of the switching system, the handover trunks 74a₁through 74a_(N) shown in FIG. 4 correspond to the handover trunks 111through 11_(N) shown in FIG. 3. The multiplexing/demultiplexing unit 71aand the header converters 72_(l1) through 72_(lN), . . . , 72_(M1)through 72_(MN) shown in FIG. 4 correspond to the radio interfaces 12₁through 12_(M). In addition, the ATM switch 73a and the headerconverters 79_(l1) through 79_(lN), . . . , 79_(M1) through 79_(MM)shown in FIG. 4 correspond to the radio transmission line forming unit13 and the remote transmission line forming unit 15 shown in FIG. 3, andthe processor 76a shown in FIG. 4 corresponds to the call processingunit 14.

FIGS. 6 and 7 are time charts for explaining the operation of thisembodiment of the switching system. Next, a description will be given ofthe operation of this embodiment of the switching system, by referringto FIGS. 5, 6 and 7.

In the radio base station 32, the radio unit 40 and thetransmission/reception amplifier 41 form a radio zone via the antenna38. Under a main control of the radio controller 36 which is provided atthe remote end via the transmission interfaces 37 and 34, the controller42 carries out a radio channel setting control with respect to the radiozone, and also carries out controls related to management, setting andrelease of the radio line of the radio base station 32 to which thecontroller 42 belongs.

In the radio line control station 31, under the radio channel settingcontrol described above, the switch part 35 carries out a diversityhandover process with respect to a plurality of radio base stationswhich are formed under control of the radio line control station 31 towhich the switch part 35 belongs. In addition, the baseband signalprocessor 39 carries out with respect to the information which isexchanged between the radio line control station 31 to which thebaseband signal processor 39 belongs and the remote mobile station (notshown) which confronts the radio line control station 31 via the antenna38, the transmission/reception amplifier 41 and the radio unit 40,modulation and demodulation processes in conformance with the CDMA,encoding and decoding processes in conformance with an error correctioncode adapted to the radio transmission line, a synchronization controlprocess, information multiplexing and demultiplexing processes, and aprocess for realizing handover synthesis process among the sectors.

The radio controller 36 is connected to the switch part 35 and thetransmission line interface 34, and confronts the remote mobile stationdescribed above via the transmission line interface 37, the basebandsignal processor 39, the radio unit 40, the transmission/receptionamplifier 41 and the antenna 38. The radio controller 36 exchangescontrol information with the remote mobile station based on the radiochannel setting control procedure described above.

On the other hand, in the ATM switching system 30, the processor 76aincludes, as station information, a radio PVC table 64 shown in FIG. 8.The VCI, the VPI and the LLN indicating the construction, that is,identification information of the partial filling cell, is registered inadvance in this radio PVC table 64, with respect to the PVCs(hereinafter referred to as radio PVCs) to be formed in correspondencewith each of the radio channels formed in the radio zone described abovein the section reaching the ports of the ATM switch 73a corresponding tothe header converters 79_(l1) through 79_(lN), . . . , 79_(M1) through79_(MM) and the handover trunks 74a₁ through 74a_(N) via themultiplexing/demultiplexing unit 71a and the header converters 72_(l1)through 72_(nN), . . . , 72_(M1) through 72_(MN).

The processor 76a includes a radio line table 65 shown in FIG. 9. Withrespect to the lines (hereinafter referred to as radio lines) which areconnected to one of the radio PVCs described above via the headerconverters 72_(l1) through 72_(lN), . . . , 72_(M1) through 72_(MN), theATM switch 73a and the header converters 79_(l1) through 79_(lN), . . ., 79_(M1) through 79_(MM), and are to be allocated to the calls and thehandover trunks 74a₁ through 74a_(N) under the resource management ofthe ATM switching system 30 to which the processor 76a belongs, theradio line table 65 stores status information B/I, call identificationinformation and channel number information, in addition to the VCI, VPIand the LLN. The status information B/I indicates whether or not theradio line is allocated to a call. The call identification informationindicates the identification information of the corresponding call whenthe status information B/I is a status B which indicates that the radioline is allocated to a call. The channel number information indicatesthe channel number indicating the radio channel which is allocated tothe call.

Furthermore, the processor 76a includes a fixed line table 66 shown inFIG. 10. With respect to the lines (hereinafter referred to as fixedlines) which are connected to the radio lines via one of the handovertrunks 74a₁ through 74a_(N), and are to be used to form the transmissionlines reaching the other party via one of the header converters 72_(l1)through 72_(lN), . . . , 72_(M1) through 72_(MN), the ATM switch 73a andthe header converters 79_(l1) through 79_(lN), . . . , 79_(M1) through79_(MM), the fixed line table 66 includes status information B/I andcall identification information, in addition to the VCI and the VPI. Thestatus information B/I indicates whether or not the fixed line isallocated to a call. The call identification information indicates theidentification information of the corresponding call when the statusinformation B/I is a status B which indicates that the fixed line isallocated to the call.

The VCI, the VPI and the LLN which are stored in the radio line table 65and he fixed line table 66 described above, are set as stationinformation similarly as in the case of the radio PVC table 64.

In the ATM switching system, when the ATM switching system 30 starts tooperate or, when one of the radio base station 32, the radio linecontrol station 31 and the multiplexing/demultiplexing unit 71a startsto operate, the processor 76a successively obtains the combination ofthe VCI, the VPI and the LLN registered in the radio PVC table 64. Inaddition, the processor 76a supplies the obtained combinations to thecommunication links (not shown) which are already provided with respectto the radio base station 32, the radio line control station 31 and themultiplexing/demultiplexing unit 71a while making the combinationscorrespond to the corresponding radio channels.

The radio base station 32, the radio line control station 31 and themultiplexing/demultiplexing unit 71a regularly form the PVCs adapted tothe VCI, the VPI and the LLN which are obtained as described above inthe sections from the radio base station 32 to the ATM switch 73a viathe radio line control station 31, the multiplexing/demultiplexing unit71a and the header converters 72_(l1) through 72_(lN), . . . , 72_(M1)through 72_(MN).

As indicated by the hatching in the radio line table 65 and the fixedline table 66 shown in FIGS. 9 and 10, the individual constructions ofthe radio line and the fixed line are preset as the station information.However, the processor 76a allocates the radio line and the fixed lineevery time the call is generated. For this reason, an initializingprocess sets a status I which indicates that no allocation is made toany of the calls with respect to all status information B/I included inthe radio line table 65 and the fixed line table 66.

On the other hand, when a mobile station 500 makes a call, for example,the mobile station 500 generates a "radio channel request" which requestallocation of the radio channel to the mobile station 500, and transmitsthis "radio channel request" to the radio base station 32 in a step (1)shown in FIG. 6.

In the radio line control station 31, the radio controller 36 reads the"radio channel request" via the antenna 38, the transmission/receptionamplifier 41, the radio unit 40, the baseband signal processor 39 andthe transmission line interfaces 37 and 34. In addition, when the radiocontroller 36 recognizes the identification information of the mobilestation 500 included in the "radio channel request", the radiocontroller 36 allocates a free radio channel with respect to the mobilestation 500. For the sake of convenience, it will be assumed that a freeradio channel having the channel number "7" is allocated with respect tothe mobile station 500. The radio controller 36 generates a "radiochannel response" which includes the channel number and the like andindicates the result of the radio channel allocation, and transmits this"radio channel response" to the mobile station 500 via the transmissionline interfaces 34 and 37, the baseband signal processor 39, the radiounit 40, the transmission/-reception amplifier 41 and the antenna 38 ina step (2) shown in FIG. 6.

A path that is used to exchange the control information between themobile station 500 and the radio controller 36 based on the radiochannel setting control procedure is the same as the path used toexchange the "radio channel request" and the "radio channel response" asdescribed above, and a reference to this path will be omitted in thefollowing description.

The mobile station 500 transmits to the radio base station 32 a "setupmessage" which indicates an originating call in a step (3) shown in FIG.6 when the "radio channel response" is recognized. The radio controller36 supplies this "setup message" to the ATM switching system 30 via theexternal interface 33 in a step (4) shown in FIG. 6.

In the ATM switching system 30, when the processor 76areceives the"setup message" via the communication links described above, theprocessor 76a makes an inquiry to a service control station (not shown)in a step (5) shown in FIG. 6 so as to determine whether or not topermit the message, with respect to the mobile station 500 at thecalling source indicated by the "setup message". Further, whenauthentication information of the corresponding mobile station 500 isreceived in a step (6) shown in FIG. 6 as a response of the servicecontrol station with respect to the inquiry, the processor 76atemporarily stores the authentication information. In addition, in orderto request information that is required to judge whether or not themobile station 500 at the source is appropriate as the subject of theservice, the processor 76a transmits a "terminal authentication request"with respect to the radio line control station 31 in a step (7) shown inFIG. 6.

The "terminal authentication request" is transmitted to the mobilestation 500 in a step (8) shown in FIG. 6 via the communication linksdescribed above, the external interface 33, the radio controller 36, thetransmission line interfaces 34 and 37, the baseband signal processor39, the radio unit 40, the transmission/reception amplifier 41 and theantenna 38.

A path that is used to exchange the control information between themobile station 500 and the processor 76a is the same as the path used toexchange the "setup message" and the "terminal authentication request"as described above, and a reference to this path will be omitted in thefollowing description.

When the processor 76a receives a "terminal authentication result" fromthe mobile station 500 via the radio base station 32 and the radio linecontrol station 31 as a response to the "terminal authenticationrequest", the processor 76a judges the appropriateness of the contentsof the "terminal authentication result" in a step (9) shown in FIG. 6based on a correlation of the contents and authentication informationwhich is stored in advance. In addition, the processor 76a when thecontents of the "terminal authentication result" is judged as beingappropriate, the processor 76a transmits a "setup response message" withrespect to the mobile station 500 in a step (10) shown in FIG. 6 toindicate the appropriateness of the contents of the "terminalauthentication result".

When the mobile station 500 recognizes the "setup response message", themobile station 500 transmits a "setup (destination number) message"which indicates the destination. In the radio line control station 31,the radio controller 36 adds the channel number of the radio channelallocated to the call prior to the "setup (destination number) message",and relays a similar "setup (destination number) message" with resect tothe ATM switching system 30.

When the processor 76a receives such a "setup (destination number)message" in a step (11) shown in FIG. 6, the processor 76a stores thechannel number included in the received "setup (destination number)message" in correspondence with the call identification information, andthereafter makes an inquiry to the service control station so as tojudge whether or not the destination is appropriate as the subject ofthe call processing. Moreover, if it is judged that the destination isappropriate as the subject of the call processing, the processor 76aacquires one of the handover trunks 74a₁ through 74a_(N) that is free ina step (12) shown in FIG. 6. For the sake of convenience, it will beassumed that the handover trunk 74a₁ is free and is acquired by theprocessor 76a.

In addition, the processor 76a makes a reference to the fixed line table66 shown in FIG. 10 and obtains a single fixed line which is free, thatis, the single fixed line having the status I as the status informationB/I. The processor 76a sets the call identification information includedin the "setup (destination number) message" as call identificationinformation corresponding to the single fixed line that is obtained, andacquires the single fixed line. In FIG. 11 which is a diagram forexplaining an embodiment of the PVC formed in this embodiment, it willbe assumed that this single fixed line that is acquired is is selectedfrom specific three lines and is defined by VPI=0 and VCI=20 asindicated by (a). In FIG. 11, those parts which are the same as thosecorresponding parts in FIG. 4 are designated by the same referencenumerals, and a description thereof will be omitted. Further, for thesake of convenience, the illustration of the radio line control station31 is omitted in FIG. 11, and only some of the header converters 72_(l1)through 72_(lN), . . . , 72_(M1) through 72_(MN) and 79_(l1) through79_(lM), . . . , 79_(M1) through 79_(MM) are shown by header converternumbers HCV1 through HCV6.

The processor 76a also makes a reference to the radio PVC table 64 shownin FIG. 8 using, as a key, the channel number included in the "setup(destination number) message", and specifies the radio PVC correspondingto the channel number. It will be assumed that this radio PVC that isspecified is defined by VPI=0, VCI=2 and LLN=5 as indicated by (b) inFIG. 11.

In addition, the processor 76a makes a reference to the radio line table65 shown in FIG. 9, and obtains a single radio line which is free, thatis, the single radio line having the status I as the status informationB/I. Further, the processor 76a sets the call identification informationand the channel number included in the "setup (destination number)message" as the call identification information and channel numbercorresponding to the single radio line, and acquires this single radioline. It will be assumed that this single radio line that is acquired isdefined by VPI=0, VCI=1 and LLN=5 as indicated by (c) in FIG. 11.

The processor 76a also supplies in addition to the radio PVC that isobtained as described above the constructions of the fixed lines and theradio lines which are indicated by VPI, the VCI, the LLN and the like,with respect to one of the header converters 72_(l1) through 72_(lN), .. . , 72_(M1) through 72_(MN) corresponding to the radio PVC, the ATMswitch 73a, one of the header converters 79_(l1) through 79_(lN), . . ., 79_(M1) through 79_(MM) and the handover trunk 74a₁. As a result, thehandover trunk 74a₁ is connected to the radio PVC via the radio line,and is also connected to the corresponding port of the ATM switch 73avia the fixed line, as one end of the transmission line reaching theother party which is specified as a result of the number analysis basedon the call processing procedure.

Further, by supplying the constructions of the radio PVC, the radio lineand the fixed line to the handover trunk 74a₁, the processor 76a startsthe handover trunk 74a₁, and transmits a "call processing message" tothe mobile station 500 in a step (13) shown in FIG. 6. This "callprocessing message" indicates the call set-up processing stage. Inaddition, the processor 76a carries out a call set-up in a step (14)shown in FIG. 6 based on a predetermined procedure by confronting theswitching system at the destination. Hence, the processor 76a provides acommunication service with respect to the call when the processor 76arecognizes that the other party responded.

When the parts of the handover trunk 74a₁ are started as describedabove, these parts carry out the following operations under the controlwhich is mainly made by the controller 63.

The line interfaces 51d and 51u carry out synchronization with respectto each of the cells obtained via the corresponding ports of the ATMswitch 73a, and carry out format conversions adapted to the processescarried out by the various parts of the handover trunk 74a₁ providedbetween the line interfaces 51d and 51u. The cell having the convertedformat is referred to as an internal cell. The cell extraction unit 52reads the internal cell which is obtained via the line interface 51d,and successively extracts the VPI, the VCI, the quality information andother control information included in the internal cell. With respect toeach internal cell, the write controller 56 obtains the controlinformation required for the storage via the cell extraction unit 52 andthe cell identifier 62. The address converter 60 successively convertsthe control information obtained by the write controller 56, includingthe cell number, the VPI and the VCI, into a write address based on theregion management carried out by the buffer manager 59. In addition, thecell buffer 53 stores the internal cell which is obtained via the cellextraction unit 52 into a storage region indicated by the write address.

The read controller 58 carries out a control related to the readoperation with respect to the cell buffer 53, based on the managementcarried out with respect to the internal cell by the cell informationmanager 57 depending on the control information obtained by the writecontroller 56 and based on the management carried out by the buffermanager 59. The management carried out with respect to the internal cellby the cell information manager 57 includes a decision to determinewhether or not the internal cell is to be the subject of the readoperation. The address converter 60 generates a read address of the cellbuffer 53 depending on the control and region management describedabove.

The header converter 61 generates the header which is to be updatedbased on the constructions of the radio PVC, the radio line and thefixed line supplied from the processor 76a via the controller 63, underthe control of the read controller 58.

The cell converter 54 successively reads the internal cell from thestorage region of the cell buffer 53 indicated by the read addressgenerated by the address converter 60, and sets the header generated bythe header converter 61 as the header of the read internal cell. Withrespect to the internal cell which is obtained in this manner, the lineinterface 51u generates a corresponding cell by carrying out a formatconversion similarly to the line interface 51d, and supplies thegenerated cell to the corresponding port of the ATM switch 73a whilemaintaining synchronism of the cells.

Accordingly, a transmission line which connects the radio line and thefixed line is regularly formed in the handover trunk 74a₁.

In addition, with respect to a radio zone adjacent to the radio zone inwhich the mobile station 500 is located, the mobile station 500 receivesin advance the radio channel the transmission quality of which is to bemanaged, and in the service state, constantly manages the transmissionquality of this radio channel. Furthermore, when the mobile station 500recognizes that the adjacent radio zone having the detected transmissionquality can be a candidate of the handover destination, the mobilestation 500 transmits a "handover request" in a step (21) shown in FIG.7. This "handover request" indicates that the adjacent zone having thedetected transmission quality can be the candidate of the handoverdestination, and includes identification information of the radio zone.

In the ATM switching system 30, the processor 76a transmits a "radiochannel allocation request" in a step (22) shown in FIG. 7 to the radiobase station (not shown) which forms the radio zone indicated by the"handover request". When the processor 76a receives a "radio channelallocation result" in response to the "radio channel allocationrequest", the processor 76a obtains a channel number indicating theradio channel included in the "radio channel allocation result". For thesake of convenience, it will be assumed that the channel number "9" isobtained as the channel number indicating the radio channel included inthe "radio channel allocation result".

In addition, the processor 76a makes a reference to the radio line table65 shown in FIG. 9, and obtains a single radio line which is free, thatis, the single radio line having the status I as the status informationB/I. Further, the processor 76a acquires the radio line by setting thecall identification information included in the corresponding "setup(remote number) message" and the channel number as the callidentification information and channel number corresponding to the radioline. In this case, it will assumed for the sake of convenience that theradio line which is acquired is defined by VPI=0, VCI=1 and LLN=6 asindicated by (e) in FIG. 11.

The processor 76a also makes a reference to the radio PVC table 64 shownin FIG. 8 using the channel number described above as the key, andspecifies in a step (23) shown in FIG. 7 the radio PVC which is formedin advance in correspondence with the candidate radio channel of thehandover destination. For the sake of convenience, it will be assumedthat the specified radio PVC is defined by VPI=0, VCI=2 and LLN=6 asindicated by (d) in FIG. 11.

Moreover, the processor 76a supplies in addition to the radio PVC thatis obtained in the above described manner the constructions of the fixedline and the radio line which are similarly obtained with respect to oneof the header converters 72_(l1) through 72_(lN), . . . , 72_(M1)through 72_(MN) corresponding to the radio PVC, the ATM switch 73a, oneof the header converters 79_(l1) through 79_(lN), . . . , 79_(M1)through 79_(MM) and the handover trunk 74a₁. The constructions of thefixed line and the radio line are indicated by the VPI, the VCI, the LLNand the like. As a result, the handover trunk 74a₁ is connected to theradio PVC which is defined by VPI=0, VCI=2 and LLN=6 via the radio linewhich is defined by VCI=1 and LLN=6.

In addition, the processor 76a transmits a "synchronization request"with respect to the mobile station 500 in a step (24) shown in FIG. 7.This "synchronization request" indicates that synchronization is to beestablished with respect to the radio channel which is the candidate ofthe handover destination. When the synchronization of the radio channelis established between the mobile station 500 and the ATM switchingsystem 30 via the radio base station and the radio line control stationwhich are not shown, the processor 76a supplies the constructions of theradio PVC and the radio line to the handover trunk 74a₁ in a step (25)shown in FIG. 7.

In the handover trunk 74a₁, the controller 63 carries out a controlrelated to the allocation of the plurality of radio lines that may beformed between the handover trunk 74a₁ and the ATM switch 73a via theline interfaces 51d and 51u. When the constructions of the radio PVC andthe radio line are received from the processor 76a, the controller 63supplies the received constructions and the constructions of the radioPVC and the radio line which are obtained before to the header converter61, the cell identifier 62 and the quality information comparator 55.

The cell identifier 62 identifies the internal cells corresponding tothe constructions of the plurality of radio lines, and notifies theidentified internal cells to the write controller 56 and the readcontroller 58. The header converter 61 carries out the headerconversions in parallel with respect to a plurality of combinations ofthe radio PVCs and the radio lines described above.

The quality information comparator 55 compares the reliabilityinformation included in the internal cells corresponding to theconstructions of the plurality of radio lines, and selects the internalcell having a maximum transmission quality indicated by the reliabilityinformation. The selected internal cell is supplied to the cell buffer53.

Accordingly, in the handover trunk 74a₁, a call signal having thehighest transmission quality is automatically selected from the callsignals which are obtained from the same mobile station 500 in parallelvia the plurality of radio zones.

In the service state, the mobile station 500 monitors thedown-transmission quality of the radio channels indicated by the channelnumbers "7" and "9" described above at a predetermined frequency. Whenthe mobile station 500 recognizes that the monitored transmissionquality has deteriorated to such an extent that the radio channel cannotbe a candidate of the handover destination, the mobile station 500transmits a "line release notification" including the identificationinformation of the corresponding radio channel in a step (26) shown inFIG. 7.

On the other hand, in the ATM switching system 30, the processor 76atransmits in a step (27) shown in FIG. 7 a "radio channel releaserequest" to the radio base station which forms the radio channelindicated by the "line release notification". For the sake ofconvenience, it will be assumed that the radio base station 32 forms theradio channel indicated by the "line release notification". When theprocessor 76a receives a "radio channel release complete notification"in a step (28) shown in FIG. 7 in response to the "radio channel releaserequest", the processor 76a obtains the channel number included in the"radio channel release complete notification".

Furthermore, the processor 76a makes a reference to the radio line table65 shown in FIG. 9 using the channel number included in the "radiochannel release complete notification" as the key, and releases thecorresponding radio line which was acquired. In other words, theprocessor 76a sets the status I in the radio line table 65 as the statusinformation B/I.

In addition, the processor 76a supplies the construction of the radioline indicated by the VPI, the VCI and the LLN to the handover trunk74a₁, and releases the connection between the handover trunk 74a₁ andthe radio line. In this case, the connection between the handover trunk74a₁ and the radio line defined by VPI=0, VCI=1 and LLN=5 is released asindicated by (c) in FIG. 11.

The processor 76a also transmits a "line release complete notification"which indicates that the link between the handover trunk 74a₁ and theradio line is released to the radio base station and the mobile station500, in a step (29) shown in FIG. 7.

According to this embodiment of the switching system, the PVCs areregularly formed between the radio channels which are independentlyallocated to the plurality of radio zones accessible by the mobilestation 500 and the handover trunks. In addition, the handover iscarried out positively and smoothly under cooperation of the selectionof the radio line that is automatically carried out by the handovertrunk based on the reliability information and the supplemental processthat is carried out by the processor 76a with regard to the setting andupdating of the selection limit.

Therefore, in this embodiment of the switching system, the processor 76amust carry out a process different from that of the conventional system,however, the load of the process related to the switching of thechannels in service, that is, the handover, is distributed among thehandover trunks 74a₁ through 74a_(N), and the response of the switchingsystem is improved.

In FIG. 11, the upper radio base station 32 makes the radio channelnumber "7" correspond to VPI=0, VCI=2 and LLN=5 for every call. On theother hand, the lower radio base station 32 makes the radio channelnumber "9" correspond to VPI=0, VCI=2 and LLN=8 for every call. The VPIis the same for each radio base station 32. With respect to the upperradio base station 32, VCI=2 specifies the PVC to the handover trunk74a₁, while VCI=4 specifies the PVC to the handover trunk 74a₂. Inaddition, with regard to the PVC, the VCI value is set as a destinationHCV value, 0 is set as the VPI value and its own HCV value HCV1 is setas the VCI value with respect to the header converter HCV1. Similarly,with regard to the PVC, the VCI value is set as a destination HCV value,0 is set as the VPI value and its own HCV value HCV2 is set as the VCIvalue with respect to the header converter HCV2. On the other hand, withregard to the SVC, the VCI value is set to 10 from 20, the VPI value isset to 0 and the HCV value is set to HCV5 with respect to the headerconverter HCV3. Similarly, with regard to the SVC, the VCI value is setto 20 from 10, the VPI value is set to 0 and the HCV value is set toHCV3 with respect to the header converter HCV5. The header converterHCV5 is coupled to another station via a trunk line.

It is a precondition in the above described embodiment that all of theradio zones are mutually adjacent or peripheral zones. However, thepresent invention is not limited to the application to such radio zones,and for example, the present invention is similarly applicable to a unitof a collection of radio zones which are formed at geographicallyscattered locations. Furthermore, in such an application, the handovertrunks 74a₁ through 74a_(N) do not need to compare the transmissionqualities with respect to the radio zones which are actually notadjacent or peripheral zones, and it is possible to avoid increase ofthe scale of the hardware that is required to make the comparison and toavoid the response of the switching system from deteriorating.

The present invention is applied to the existing ATM switching system inthe above described embodiment, but the application of the presentinvention is not limited to the ATM switching system. For example, thepresent invention is similarly applicable to a Synchronous Transfer Mode(STM) switching system as long as a desired and high response can besecured with respect to the switching of the channels in service, thatis, the handover.

Furthermore, a description of a trunk which is used to provide a servicewith respect to a call which does not require the handover, such as acall generated from a terminal which is fixedly set up, and adescription of a call processing which is carried out by mainlycontrolling such a trunk, will be omitted in this specification becausesuch trunk and call processing are known and are not directly related tothe subject matter of the present invention.

In the embodiment described above, the radio transmission lines areformed via the ATM switch 73a and the header converters 79_(l1) through79_(lN), . . . , 79_(M1) through 79_(MM), between the header converters72_(l1) through 72_(lN), . . . , 72_(M1) through 72_(MN) and thehandover trunks 74a₁ through 74a_(N). However, the present invention isnot limited to such a construction, and for example, the radiotransmission lines may be formed via a hardware which is independent ofthe ATM switch 73a.

The embodiment is described for a case where there are two radio zoneswhich are candidates of the handover destination, but the number ofcandidates of the radio zones is of course not limited to two and thenumber of candidates may be three or more.

Moreover, in the above described embodiment, the radio PVCscorresponding to all of the radio channels are fixedly allocated to thecalls. However, when the "call processing message" is received, forexample, the radio controller 36 of the radio line control station 31may dynamically set the corresponding relationship of the radio channelsand the radio PVCs which are used for the service.

Next, a description will be given of a communication system applied withthe present invention. FIG. 12 is a system block diagram showing thecommunication system applied with the present invention.

In FIG. 12, the communication system includes a common line signalnetwork 200, a STM/ATM network 201, switching nodes 202, a switchingnode 203, a known switching node 204, a known switching node 205, aplurality of base stations 301, and a plurality of CDMA stations 302which are coupled as shown. In FIG. 12, a solid line indicates a STMline, a bold solid line indicates an ATM line, and a bold dotted lineindicates a control signal line to the common line signal network 200.

The switching node 202 includes the switching system of the presentinvention, such as the ATM switching system 30 shown in FIG. 4. Thisswitching node 202 is coupled to the common signal line network 200 viathe control signal line, and is coupled to the STM/ATM network 201 viathe STM and ATM lines. This switching node 202 is further coupled to theother switching nodes 202 and 203 via the ATM lines, and is also coupledto the known switching node 205 via the STM line. The base stations 301can be coupled to the switching node 202 via the STM lines, and the CDMAstations 302 can be coupled to the switching node 202 via the ATM lines.

The switching node 203 includes the switching system of the presentinvention, such as the ATM switching system 30 shown in FIG. 4. Thisswitching node 203 is coupled to the common signal line network 200 viathe control signal line, and is coupled to the STM/ATM network 201 viathe STM and ATM lines. This switching node 203 is further coupled to theother switching nodes 202 via the ATM lines, and is also coupled to theknown switching node 205 via the STM line.

The known switching node 204 is coupled to the base stations 301 and theother known switching node 205 via the STM lines. This known switchingnode 204 is also coupled to the common signal line network 200 via thecontrol signal line. On the other hand, the known switching node 205 iscoupled to the common signal line network 200 via the control signalline, and is coupled to the STM/ATM network 201 via the STM line.

When the switching system of the present invention is applied to thecommunication system shown in FIG. 12, it is possible to flexibly copewith frequent generation of handovers, without requiring a considerablemodification of the existing hardware forming the switching nodes.

Further, the present invention is not limited to these embodiments, butvarious variations and modifications may be made without departing fromthe scope of the present invention.

What is claimed is:
 1. A switching system comprising:N handover trunksrespectively having M terminals to be independently coupled to radiotransmission lines reaching M radio base stations which respectivelyform radio zones which become mutually adjacent zones or peripheralzones, and coupled to remote transmission lines reaching mobile stationsof other parties located in the radio zones, where M and N are integersgreater than one, out of the radio transmission lines, said N handovertrunks selecting each transmission line with a best transmission qualityand coupling the selected radio transmission lines to the remotetransmission lines; a plurality of radio interfaces distributing linesindependently formed between the switching system and the M radio basestations, with respect to different N paths; a radio transmission lineforming unit forming radio transmission lines in advance with respect toall combinations of each of the paths subject to the distribution bysaid radio interfaces and each of the terminals other than the terminalsto be independently coupled to the remote transmission lines out of theterminals of said handover trunks; a call processing unit carrying out acall processing with respect to calls generated by the mobile stationslocated in the radio zones by cooperating with a radio channel settingcontrol that is carried out by the radio base stations via said radiointerfaces; and a remote transmission line forming unit forming theremote transmission lines by the call processing carried out by saidcall processing unit.
 2. The switching system as claimed in claim 1,which further comprises:a storage unit which is registered in advancewith a set of radio zones corresponding to the adjacent zones or theperipheral zones, with respect to each of the radio zones formed by theradio base stations, said call processing unit including means forobtaining the radio zone where the mobile station which generated thecall is located or is predicted to be located, with respect to each ofthe calls subject to the call processing, and for notifying the radiozones registered in said storage unit with respect to the obtained radiozone to at least one of said handover trunks coupled to the radiotransmission line, said handover trunks selecting the radio transmissionline having the best transmission quality by limiting candidates to theradio transmission lines corresponding to the radio zones notified bysaid call processing unit.
 3. The switching system as claimed in claim2, wherein said radio transmission line forming unit and said remotetransmission line forming unit are integrally formed as a single unit,so as to form the radio transmission lines by the call processingcarried out by said call processing unit.
 4. The switching system asclaimed in claim 2, wherein said radio transmission line forming unitand said remote transmission line forming unit are formed independentlyas separate units, so as to automatically form all of the radiotransmission lines.
 5. The switching system as claimed in claim 2,wherein an asynchronous transfer mode is applied to the plurality oflines formed between said radio interfaces and the plurality of radiobase stations, so that said radio transmission line forming unit formsthe radio transmission lines conforming to the asynchronous transfermode.
 6. The switching system as claimed in claim 2, wherein said radiotransmission line forming unit and said remote transmission line formingunit are integrally formed as a single unit, so as to form the radiotransmission lines by the call processing carried out by said callprocessing unit.
 7. The switching system as claimed in claim 6, whereinan asynchronous transfer mode is applied to the plurality of linesformed between said radio interfaces and the plurality of radio basestations, so that said radio transmission line forming unit forms theradio transmission lines conforming to the asynchronous transfer mode.8. The switching system as claimed in claim 2, wherein said radiotransmission line forming unit and said remote transmission line formingunit are formed independently as separate units, so as to automaticallyform all of the radio transmission lines.
 9. The switching system asclaimed in claim 8, wherein an asynchronous transfer mode is applied tothe plurality of lines formed between said radio interfaces and theplurality of radio base stations, so that said radio transmission lineforming unit forms the radio transmission lines conforming to theasynchronous transfer mode.
 10. The switching system as claimed in claim1, wherein said radio transmission line forming unit and said remotetransmission line forming unit are integrally formed as a single unit,so as to form the radio transmission lines by the call processingcarried out by said call processing unit.
 11. The switching system asclaimed in claim 10, wherein an asynchronous transfer mode is applied tothe plurality of lines formed between said radio interfaces and theplurality of radio base stations, so that said radio transmission lineforming unit forms the radio transmission lines conforming to theasynchronous transfer mode.
 12. The switching system as claimed in claim1, wherein said radio transmission line forming unit and said remotetransmission line forming unit are formed independently as separateunits, so as to automatically form all of the radio transmission lines.13. The switching system as claimed in claim 12, wherein an asynchronoustransfer mode is applied to the plurality of lines formed between saidradio interfaces and the plurality of radio base stations, so that saidradio transmission line forming unit forms the radio transmission linesconforming to the asynchronous transfer mode.
 14. The switching systemas claimed in claim 1, wherein an asynchronous transfer mode is appliedto the plurality of lines formed between said radio interfaces and theplurality of radio base stations, so that said radio transmission lineforming unit forms the radio transmission lines conforming to theasynchronous transfer mode.